As the photodetecting device, the one including a photodiode and an integrating circuit is known (for example, see Patent Document 1). This integrating circuit includes an amplifier circuit having a first input terminal, a second input terminal, and an output terminal; and a capacitive element and a switch provided between the first input terminal and the output terminal of the amplifier circuit, the capacitive element and the switch being connected in parallel to each other. In this photodetecting device, the switch of the integrating circuit is closed so that the capacitive element in the integrating circuit is discharged, and the voltage value output from the integrating circuit is initialized. When the switch of the integrating circuit is opened, an electric charge generated in the photodiode is accumulated in the capacitive element of the integrating circuit, and a voltage value according to the amount of accumulated electric charge is output from the integrating circuit. Further, if the photodetecting device includes a plurality of photodiodes arranged in one dimension or in two dimensions, it is possible to obtain an optical image in one dimension or in two dimensions.